The garden pea (Pisum sativum L.) is a commercially important food crop and the immature seed of the garden pea ("peas") are widely consumed. There are a large number of genes that affect peas. The first reported and best described gene is the r gene (see White, O. E., Proceedings of the American Philosophical Society, 56: 487-588). The r mutant is believed to have occurred spontaneously at the beginning of the seventeenth century (see Lamprecht, H., Agri. Hortique Genetica 14: 1-4 (1956)) and its mature, dry seed has a wrinkled appearance (hence "r", derived from the Latin, rugosus meaning "wrinkled or shriveled"). Wrinkling of mature seed was one of the characteristics used by Mendel in experiments which led him to formulate his laws of inheritance. (see Mendel, G., Verhandlungen des naturforshenden Vereinds in Brunn 4: 3-47 (1865)). A second gene, referred to as rb, has also been identified. Mature seeds homozygous for rb also exhibit a wrinkled appearance.
Genes at the rugosus loci, R and Rb, are known to affect the development of embryos directly in peas. (see Wang, T. L., et al., Plant Breeding 105: 311-320 (1990)). The R locus has been shown to encode one form of the starch branching enzyme. Id. Genes at the R and Rb loci are pleiotropic, affecting the level and type of starch, other storage products, the osmotic environment of the embryo and the growth of the embryo. (see Wang, T. L., et al., "New Mutants for Seed Development in Peas" in IPSR & JIC Annual Report (1992)).
Sweetness, such as sucrose content, in peas, is generally prized by consumers, who perceive that sweeter peas have a better flavor. Thereupon, because peas are such an important food crop, there is a need in the art for peas having an increased sweetness.